1. Field of the Invention
The present invention relates to a laser drive device, laser light emitting device and a laser driving method, and it particularly relates to a laser drive device and a laser driving method for controlling an output of a laser element or a current to be supplied to the laser element, and a laser light emitting device provided with the laser drive device.
2. Description of the Related Art
In recent years, in the laser processing technology field of welding and quenching, etc., a replacement of a solid laser, such as a gas laser and a YAG, with a high-power semiconductor laser has progressed. Further, semiconductor lasers are expected to be applied to medical fields.
FIG. 10 is a view showing a relationship between a current to be supplied to a semiconductor laser and a light output.
When a current is applied to a semiconductor laser and exceeds an oscillation start current (oscillation threshold current value), laser oscillation starts. As the applied current is further increased, the resultant light output also increases, however, when the applied current reaches a certain value, the resultant light output decreases. This phenomenon is caused that the light output at an output end face (chip end face) of the semiconductor becomes excessive and the output end face is subjected to catastrophic optical damage (COD).
To prevent the arising of the COD, a rated output value “Po” is normally set to be about half of a light output value Pcod at which the COD occurs. The semiconductor laser is used within a range of the rated output value by a user.
However, in the laser processing technology field, as mentioned above, it suffers from a disadvantage that even when using the semiconductor laser within the range of the rated output value Po, a reflected light from an object to be processed again is again input into the semiconductor laser as a returned light, and the returned light results in a deterioration or failure of the semiconductor laser.
See, (1) Yoshio Takiguchi, et al. “Characteristics of Broad-Area Laser Diodes with Optical Feedback” Digests of Lectures of Association Conference of Applied Physics, Spring 2004, and (2) Yoshio Takiguchi, et al. “Characteristics of Broad-Area Laser Diodes with Optical Feedback II (λ=640 nm)” Digests of Lectures of Association Conference of Applied Physics, Autumn 2004
The disadvantage is caused because, in the laser processing field, a high-power (W class) semiconductor laser is used and an affection by the returned light cannot be ignored. Also, in the laser processing field, an amount of the returned light from an object to be processed may become very large depending on the use condition by the user.
Since the affection by the returned light was not considered for defining the rated output value in the related art, the rated output value was not always applied as a value for guaranteeing the prevention of deterioration or failure of the laser element depending on the use condition by the user.